Adolescent substance use is prevalent and associated with a broad range of adverse outcomes such as poorer academic performance, risky sexual behavior, mental health problems and increased risk of developing a substance use disorder. The aim of the proposed research is to pilot test a universal intervention to prevent substance use in youth by improving sleep. This indirect approach to substance use prevention is predicated on several lines of evidence: a) few programs directly targeting prevention of substance use in high school populations have been found to be effective, b) multiple cross-sectional and prospective studies have reported that insufficient sleep in youth predates and predicts substance use, c) multiple modifiable factors contribute to the current epidemic of insufficient sleep among youth (e.g., use of technology late into the night, irregular sleep-wake schedules from weekdays to weekends) and d) previous sleep interventions for youth have yielded promising results for improving sleep. We will pilot the 'Sleep Fitness' (SF) intervention. SF is an 8 session, scale-able, school-based prevention program for urban adolescents attending 9th grade (ages 14 to 16; n=300). The SF intervention draws on empirically- supported interventions for sleep problems, adapted to be effective in promoting healthful sleep patterns. The study uses a cluster-randomized experimental design (randomized at classroom level) in schools to test our hypotheses that the SF intervention will be more effective than a Psycho-education (PE) control condition in achieving improvements in sleep, substance use, and selected mental health outcomes (anxiety, depression). Outcome measures will be assessed at baseline, post-intervention, and 6 and 12 months later. We will further examine if reductions in substance use are mediated by improvements in sleep and mental health. All outcome analyses will control for perceived stress. The research conducted as part of this R34 application is intended to inform future large-scale testing of the intervention via: a) Establishig the feasibility of the intervention, study design, and measures in diverse high school settings; b) Generating initial effect size estimates for outcomes and potential moderators; and c) Further adaptation of the intervention for maximal effectiveness, including involvement of students at each school to clarify motivational levers for behavior change. The proposed program of research is the first to test a universal intervention to promote sleep as a means of reducing substance initiation and use. If positive, the findings will have major public health implications or adolescent health promotion as well as for the interactive relationships among sleep, substance use, and mental health among urban teenagers.